Social Networks Over Time and the Invariants of Interaction

We are all embedded within social networks. Who we interact with can affect the choices we each make as individuals. Therefore, if we can quantitatively study social networks, we can better understand human behavior.

We collaborated with the folks at Gallup to do a longitudinal survey of people’s social networks. Of course, we’re unable to determine the complete social structure of the United States (we’ll leave that to the Data team at Facebook), so we sampled a representative population of several thousand Americans and examined their close social contacts, how each person’s contact are connected to each other, and how this changes over time. [As an aside, if you are in the market for a good social network survey tool, talk to Gallup. I think we developed a pretty awesome tool.]

Recapitulating other classic research, we found that the average number of close social contacts (like a spouse or good friend, not just your acquaintances) is only about four. But we also were able to determine how these network connections (number/degree and closeness), as well as how friends are connected to each other (transitivity), changed over time. Some of the findings about social ties over time are summarized in this chart below:

We found some interesting results. The most intriguing is an invariant in our interactions: just as Dunbar’s Number limits our social connections, there is also a clear relationship between the closeness to one’s social contacts and the total number of contacts you have.

Just as there are certain cognitive limits to the number of individuals one can have as part of one’s social network, it also appears that there are cognitive and temporal considerations for how humans manage their interactions. In particular, we find that the reported average closeness to all friends decreases as the number of one’s friends increases, suggesting an invariant total expenditure on social interaction [emphasis added]. An increase of one in the number of close social contacts was associated with a decrease of 0.03 in the average closeness of each individual contact on a scale where 0 = do not know and 1 = extremely close. An increase of two close contacts was associated with a decrease in closeness of nearly 0.06 (a substantial reduction on this scale). Because, in prior research, ties are typically modeled as either present or absent, with no strength information, these findings are some of the first of their kind.

In addition, we surveyed the respondents about their health and various pro-social behaviors (such as giving blood). And we found that these are related to our social networks. Specifically, “having more friends is associated with an improvement in health, while being healthy and prosocial is associated with closer relationships. Specifically, a unit increase in health is associated with an expected 0.45 percentage-point increase in average closeness, while adding a prosocial activity is associated with a 0.46 percentage-point increase in the closeness of one’s relationships.”

We are embedded within networks, which are related to how we help others, and even to our health. But these network connections are not unbounded: we have a finite social attention span. As we gain more friends, we become less close to all of them. So this embeddedness in networks is a precious thing. Understand the implications of social connections and use them wisely.

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